1. Field of the Invention
The present invention relates to an exposure calculation device for a camera, which calculates an exposure value from photometric data obtained by divided photometry of light transmitted through a photographic lens.
2. Description of the Related Art
In Japanese Patent Laying-Open Publication 57-84441 a camera is disclosed which, using a CCD or a MOS or the like type of image sensor, obtains an exposure value for the camera by dividing up the photographic field finely and into a large number of regions and by performing photometry on the divided photographic field.
However, with a sensor of the type in which the outputs of the photoelectric device are accumulated as electric charges for a predetermined time period and then the accumulated charges are read out in order, since a relatively high bias voltage is supplied to the photoelectric device, the dark current is increased, and the noise level is elevated, and the problem arises that the photometric capability in low luminance is bad. This problem becomes particularly great in a high temperature situation.
Further, in U.S. Pat. No. 4,977,424, a camera is disclosed in which, along with obtaining photometric data by performing photometry on light transmitted through the photographic lens, a compensation value is calculated for the above described photometric data based upon the exit pupil and the open aperture value of the photographic lens, and an exposure value is calculated according to the photometric data corrected according to this compensation value. Here, the exit pupil and the open aperture value may for example be read in from an in-lens ROM included in the photographic lens.
However, in the case of so called divided photometry in which photometry is performed by dividing up the photographic field into a plurality of photometric regions, since it is necessary to calculate the above described compensation values for each of the plurality of photometric regions, not only does the time period for compensation calculation of the photometric data by the compensation values become increased, but also the cost is increased because it becomes necessary to provide a memory of high capacity for recording the compensated plurality of photometric data items. Further, with a divided photometric device, because the amount of light arriving at a portion corresponding to the peripheral portion of the photographic plane is low in comparison with the central portion, the problem arises that the reliability is deteriorated, since the finer the division of the element becomes, the larger become the compensation values corresponding to the photometric data from the peripheral portion.